Knowledge and Management of Aquatic Ecosystems (2011) 401, 10 http://www.kmae-journal.org c ONEMA, 2011 DOI: 10.1051/kmae/2011024 Review A review of ecological interactions between crayfish and fish, indigenous and introduced J.D. Reynolds(1) Received January 17, 2011 Revised March 14, 2011 Accepted March 16, 2011 ABSTRACT Key-words: Crayfish (decapods) and fish are both long-lived large members of fresh- crayfish, water communities, often functioning as keystone species. This paper freshwater fish, reviews interactions between these, with emphasis on the European con- keystone text. Native crayfish and fish are in ecological balance, which may involve species, mutual predation, competition and sometimes habitat disturbance. This competition, balance is disrupted by range extensions and translocations of native predation, fish or crayfish into exotic situations. Some fish and crayfish have been translocation, translocated globally, chiefly from North America to other continents. Non- alien invasive indigenous crayfish species (NICS) may impact on native fish, just as in- species, troduced fish impact on indigenous crayfish species (ICS). Competition native species between ICS and NICS may result in making the former susceptible to various mechanisms of interaction with fish, indigenous or introduced. In Europe, long-established NICS – signals, spiny-cheek and red swamp crayfish – may occur in greater densities than ICS; they are more tolerant and aggressive and show more interactions with fish. More recent intro- ductions, still restricted in distribution, have not yet received enough study for their impacts to be assessed. Interactions between fish and crayfish in North and South America, Madagascar and Australasia are also explored. Mechanisms of interaction between fish and crayfish include mutual pre- dation, competition for food and spatial resources, food-web alteration and habitat modification. Resultant changes in communities and ecosys- tems may be physical or biotal, and affect both ecosystem services and exploitation potential. RÉSUMÉ Interactions écologiques entre les écrevisses et les poissons, indigènes et introduits Mots-clés : Les écrevisses (décapodes) et les poissons appartiennent aux grandes commu- écrevisses, nautés d’eau douce à longue durée de vie et fonctionnent souvent comme des poissons espèces clés. Cet article synthétise la littérature sur les interactions entre pois- d’eau douce, sons et écrevisses, en mettant l’accent sur le contexte européen. Les écrevisses espèces clés, et les poissons autochtones sont en équilibre écologique, ce qui peut impliquer compétition, la prédation mutuelle, la compétition et parfois la perturbation des habitats. Cet prédation, équilibre est perturbé par l’extension de leur distribution et les transferts de pois- sons indigènes ou d’écrevisses dans des situations exotiques. Certains poissons et écrevisses ont été transférés au niveau mondial, principalement de l’Amérique (1) Trinity College, Dublin University, 115 Weirview Drive, Stillorgan, Co. Dublin, Ireland, [email protected] Article published by EDP Sciences J.D. Reynolds: Knowl. Managt. Aquatic Ecosyst. (2011) 401, 10 translocation, du Nord vers d’autres continents. Les espèces d’écrevisses non indigènes (NICS) espèces peuvent avoir un impact sur les poissons indigènes, et inversement les poissons exotiques non indigènes sur les espèces d’écrevisses indigènes (ICS). La concurrence entre invasives, ICS et NICS peut se traduire par leur sensibilité à divers mécanismes d’interaction espèces avec les poissons indigènes ou introduits. En Europe, les écrevisses non indigènes indigènes (NICS), établies de longue date (écrevisse signal, écrevisse américaine et écre- visse rouge de Louisiane), peuvent avoir des populations de plus grande densité que celles des écrevisses indigènes (ICS) ; elles sont plus tolérantes et agressives et montrent plus d’interactions avec les poissons. Les espèces introduites plus ré- cemment, et encore limitées dans leur distribution, n’ont pas encore fait l’objet de suffisamment d’études pour pouvoir évaluer leurs impacts. Les interactions entre les poissons et les écrevisses en Amérique du Nord et du Sud, en Madagascar et en Australasie sont également analysées. Les mécanismes d’interaction entre les poissons et écrevisses comprennent la prédation mutuelle, la compétition pour la nourriture et les ressources spatiales ainsi que la modification du réseau trophique et de l’habitat. Les changements qui en résultent, en ce qui concerne les commu- nautés et les écosystèmes, peuvent être physiques ou biotiques et affecter à la fois les services écosystémiques et le potentiel d’exploitation. INTRODUCTION Fish are often considered to control the structure of freshwater systems. However, decapods (crayfish and crabs), as the largest active predatory or broadly omnivorous invertebrates in many freshwater systems, are also capable of dominating secondary production and biomass (Geiger et al., 2005;Gherardi,2007; Reynolds and Souty-Grosset, 2011). In Europe and North America crayfish have long been known to affect habitats and communities (e.g. Abrahamsson, 1966; Lorman and Magnuson, 1978; Momot et al., 1978). For example, in a range of North American ponds, crayfish had both direct and indirect community effects on the biomass of zooplankton and phytoplankton assemblages and peak levels of dissolved oxygen, also strong negative effects on macrophyte establishment, metaphyton abundance and composition, gastropod biomass, and the density of bullfrog tadpoles (Dorn and Wojdak, 2004). These and other studies suggest that lakes and ponds with abundant crayfish will be structurally comparatively simple, with few macrophytes and gastropods. In such systems some species of amphibians and fish will perform poorly, while other organisms may benefit (Dorn and Wojdak, 2004). Freshwater decapods often coexist with fish in streams and lakes, although other situations where crayfish live, including swamps and temporary wetlands, may not support fish. Both decapods and fish may control community biodiversity through their large size, longevity and trophic specializations. They may also act as ecosystem engineers; they are thus keystone species. Size helps in dominance, while longevity means a long environmental memory, so intermittent or occasional adverse environmental situations can have long-lasting impacts on populations. There are over 550 species of freshwater crayfish, widely distributed across the globe, chiefly in temperate and subtropical water bodies and wetlands. Freshwater crabs (over 1100 species, many restricted or endemic) occur predominantly in tropical streams and lakes and are rarely sympatric with crayfish, although Potamon spp. crabs overlap with white-clawed crayfish Austropotamobius pallipes in southern Europe (Barbaresi and Gherardi, 1997). However, the invasive diadromous mitten crab Eriocheir sinensis is increasingly enter- ing the native ranges of several temperate crayfish species. Some crayfish have expanded their distributional ranges; others have been widely translocated beyond their normal range, such as the thin-clawed crayfish Astacus leptodactylus to western Europe (Souty-Grosset et al., 2006), and still others have been introduced to many land areas overseas, e.g. sig- nal crayfish Pacifastacus leniusculus and red swamp crayfish Procambarus clarkii from North 10p2 J.D. Reynolds: Knowl. Managt. Aquatic Ecosyst. (2011) 401, 10 America to Europe, Africa and Asia (Holdich et al., 2009b). In their new locations, these non- indigenous crayfish species (NICS) must be distinguished from indigenous crayfish species (ICS). The number of freshwater fish has been variously estimated between 9000 and 25 000 species, with a median estimate of around 16 000 species. Largely because of their commercial interest, many species of fish have been translocated or introduced around the globe, thus tilapias have been moved from Africa throughout the tropics, carps across Eurasia and northern hemisphere salmonids introduced to South America, South Africa, Tasmania and New Zealand. Within Eurasia, cyprinid and percoid fishes have been widely established outside their native ranges. All these moves have had major community consequences. There has been an alarming decline in crayfish populations worldwide, recently documented by IUCN (see, for example, Edsman et al., 2010; Füreder et al., 2010). Many factors have been implicated in this decline, among them deteriorating aquatic environments, waterborne bio- cides and toxins, overfishing and disease. In addition, recent decades have seen an enormous expansion in global translocations of organisms, leading to novel ecological situations involv- ing changed balances of competition and predation. Alien predatory fishes may negatively impact on native crayfish, while fish populations may be affected by predation and competi- tion from various types of organisms, including exotic crayfish (Degerman et al., 2007). Mechanisms of interactions between fish and crayfish may be direct, e.g. predation or com- petition, or indirect, through alteration of habitats and interactions with the ecosystem, such as through bird and mammal predators or through food-web manipulation leading to changed littoral communities. Competitive interactions have two main focuses, food and shelter. When both decapods and co-existing fishes are omnivorous there will be competition and mu- tual predation, depending on relative size and vulnerability. Reciprocal uses may reflect such trophic interactions; crayfish are often used as bait for sport fish, while